(Reuters) - The NFL’s concussion protocol was brought into question on Sunday when Houston Texans quarterback Tom Savage appeared to suffer a temporary lack of consciousness against the San Francisco 49ers but was allowed to play on.

Savage took a devastating hit from 49ers defensive end Elvis Dumervil during the second quarter and could be seen trembling with his arms stiffened and outstretched.

The QB made his way back into the game for his team’s next series before ultimately being replaced by backup T.J. Yates.

Following the game, Texans coach Bill O’Brien was questioned on why Savage was allowed by return to the game after sustaining the hit.

“We evaluated him, at that time and made the determination that he was OK,” O’Brien told reporters.

“Not me, obviously, the evaluators made the determination to put him back in the game. He went back in the game and came out and they evaluated him a little bit more just because of what they saw. And that’s where it’s at.

“That’s all I really know about it.”

The controversial clearance of Savage to play is likely to lead to further calls for a review of the NFL’s concussion procedure as a whole.